It is known that aircrafts are able to manage a time constraint while modulating their speed. The flight management system of the Flight Management System (“FMS”) type, should be able to ensure the function of fulfilling a time constraint at a given waypoint. To this end, it calculates optimum parameters, including in speed, so as to reach the specified waypoints at the expected time. A speed strategy should be defined throughout the flight plan in order to optimize the arrival at the constraint.
The flight management system calculates its predictions through comparing the time constraint Required Time of Arrival (“RTA”) with an estimated time of arrival Estimated Time of Arrival (“ETA”), being directly linked to the speed. If the estimated time of arrival is lower than the time constraint, the flight management system recalculates a speed profile so as to slow down (and vice versa), the aim being converging the estimated time ETA to the constraint RTA.
The issue linked to the constraint RTA results from the fact that calculating the speed profile uses a large part of the calculation abilities of the flight management system. The process for calculating predictions comprises an iterative loop allowing for the convergence, but requiring a large calculation capacity from the embedded computer. As it is already demanding for the system to carry out the calculations for one single constraint, it is technically difficult to impose multiple RTA constraints (several successive time constraints) and to calculate the adapted speed profiles, currently, as a result of the technical limitations at the level of the embedded computer.
The present invention aims at indicating to the pilot(s) beforehand (before the first time constraint) whether the aircraft is able to fulfill the next constraints in the case of several successive time constraints.
It is also necessary to be able to manage multiple constraints in the case where constraints defined as time windows should be fulfilled, making the problem even more complex. In this case, this is no longer a conventional constraint RTA for which the aircraft is requested to arrive at a waypoint on a precise time. In such a case, it is requested that it should arrive at this waypoint in a given time interval. Thus, if the aircraft arrives at any moment of this interval, the constraint is fulfilled, otherwise not. In the case of time windows, there are numerous possible speed profiles allowing the constraint to be fulfilled.
Moreover, in this situation, it can also happen that a speed profile allowing the first constraint to be respected could lead to the impossibility of fulfilling the second constraint or a next constraint.
Indeed, the embedded computer calculates an adapted speed profile so as to reach the first constraint in the imparted time window. However, as this constraint is a window, it optimizes the speed with the only aim to fulfill the first constraint, and before arriving within the time interval. It does not take into consideration the following constraints. Indeed, it could only calculate an optimized speed profile for the first constraint. Thus, in an extreme case, it could happen that it selects a speed profile subsequently preventing it from respecting the next constraints while respecting the first constraint. For example, if the second time constraint is tight, it requires arriving at the point of the first constraint in a tighter time window than this first constraint. But the system, not taking into consideration the speed profile for the second constraint, could very well decide to apply a slow speed profile (in order to save fuel, for instance) that will allow it to arrive very late up to the constraint so that it is impossible to catch up the delay for fulfilling the second constraint.
Thus, without the complete calculation of the speed profile throughout the whole flight plan, up to the last time constraint, it becomes impossible to know whether a plurality of successive time constraints are fulfilled or not.
The present invention aims at overcoming the above mentioned drawbacks and providing an operator, including a pilot of the aircraft, with a piece of information relating to fulfilling successive time constraints, before even the first constraint has been reached, and this without having to calculate the speed profile until the last constraint. More precisely, the present invention relates to a method for checking whether, upon a flight of an aircraft, the latter is able to fulfill a plurality of successive time constraints, each of which is relative to a required time of arrival in a particular waypoint.